Inertial navigation units may be employed for location determination. For example, an inertial navigation unit may be carried by an individual such that the individual can determine his/her position by reference to the inertial navigation unit. As another example, an inertial navigation unit may be mounted upon or otherwise carried by a vehicle or other structure that is configured to move or be repositioned such that the position of the vehicle or other structure may be determined by reference to the inertial navigation unit.
While inertial navigation units may be widely used on the surface, some inertial navigation units may be deployed in underground applications, such as in underground tunnels, caverns or other subterrarian facilities. These inertial navigation units that are deployed underground may, for example, be carried by individuals who are underground or mounted upon or otherwise carried by vehicles or other structures that are deployed underground. The location information provided by inertial navigation units that are deployed in underground applications may be particularly helpful, as there may be fewer landmarks or other sources of location information underground than there are for surface-based applications.
An inertial navigation unit generally utilizes a plurality of accelerometers and gyroscopes to determine via dead reckoning the position, orientation and velocity without the need for an external reference. While the location that is initially determined by an inertial navigation unit may be relatively precise, the error associated with the location that is determined by the inertial navigation unit may grow or accumulate over time. Thus, the location that is determined by an inertial navigation unit that has been operational for some period of time may be less reliable than is desired for some applications.